• Chinese Journal of Lasers
  • Vol. 49, Issue 13, 1315002 (2022)
Zhilun Zhang1, Xianfeng Lin1, Wenzhen Li1, Zhongwei Xu2, Lei Liao2, Gui Chen1, Yingbo Chu1, Yingbin Xing1, Haiqing Li1, Jinggang Peng1, Nengli Dai1, and Jinyan Li1、*
Author Affiliations
  • 1Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
  • 2Wuhan Changjin Laser Technology Co. Ltd., Wuhan 430206, Hubei, China
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    DOI: 10.3788/CJL202249.1315002 Cite this Article Set citation alerts
    Zhilun Zhang, Xianfeng Lin, Wenzhen Li, Zhongwei Xu, Lei Liao, Gui Chen, Yingbo Chu, Yingbin Xing, Haiqing Li, Jinggang Peng, Nengli Dai, Jinyan Li. 4 kW Near-Diffraction-Limit Laser Output Based on Low-Numerical Aperture Confined-Doped Long-Tapered Fiber[J]. Chinese Journal of Lasers, 2022, 49(13): 1315002 Copy Citation Text show less

    Abstract

    Objective

    High-power ytterbium-doped fiber lasers (YDFLs) have good beam quality, high conversion efficiency, high reliability, and good compactness, making them widely usable in industrial processing, military, and national defense fields. The output power of YDFLs has been unprecedentedly improved with the development of double-clad fiber, laser diodes, and passive devices. This unprecedented progress is hampered by nonlinear effects, such as stimulated Raman scattering (SRS) and transverse mode instability (TMI). The most effective and fundamental way to suppress these two effects is to optimize the structure design of active fiber. We propose a low-numerical aperture confined-doped long-tapered (LCT) fiber that combines the advantages of low numerical aperture (NA), Yb3+ ions restricted doping, and longitudinal tapered design and can theoretically suppress TMI and SRS effects simultaneously.

    Methods

    The LCT fiber is proposed and successfully fabricated using modified chemical vapor deposition (MCVD) in conjunction with a solution doping technique (SDT). The LCT fiber has a core NA of ~0.05 and a gain dopant doping diameter ratio of ~77%, with a core/cladding diameter of 25/400 μm at both ends and 37.5/600 μm in the middle. A bidirectional-pumped master oscillator power amplifier (MOPA) system verifies the laser performance of the LCT fiber.

    Results and Discussions

    A laser output of 4.188 kW was obtained with a slope efficiency of 82.8% (Fig. 3). The intensity of the Raman Stocks light was ~18 dB lower than that of the signal laser at 4.188 kW output power, and the M2 factor was about 1.3, maintaining a single-mode output. Further optimization will focus on improving the pump absorption and effective mode area of this fiber to mitigate SRS.

    Conclusions

    We present a novel low-NA (0.05) confined-doped long-tapered fiber fabricated using the MCVD process in conjunction with SDT. The Yb-ions doping diameter ratio is ~77%, and the middle section core/cladding diameter is 37.5/600 μm, tapering to 25/400 μm at both ends. In the bidirectional pumping MOPA configuration, a 4.188 kW laser is obtained with a slope efficiency of 82.8%. The M2 factor is about 1.3 at 4.188 kW output power, maintaining a single-mode output. The results above reveal that using low-NA confined-doped long-tapered Yb-doped fiber to achieve high power output with high brightness is a promising prospect.

    Zhilun Zhang, Xianfeng Lin, Wenzhen Li, Zhongwei Xu, Lei Liao, Gui Chen, Yingbo Chu, Yingbin Xing, Haiqing Li, Jinggang Peng, Nengli Dai, Jinyan Li. 4 kW Near-Diffraction-Limit Laser Output Based on Low-Numerical Aperture Confined-Doped Long-Tapered Fiber[J]. Chinese Journal of Lasers, 2022, 49(13): 1315002
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